Phillips was co-founder and first chairman of the Legal Action Group in 1971, and also in the same year co-founded the The Parlex Group of trans-Europe lawyers.[1] He co-founded the Solicitors Pro Bono Group (LawWorks) in 1996, becoming President.[1]

Following his frustrations of people's lack of knowledge about their rights and responsibilities as citizens, Phillips secured funding from The Law Society to set up the Law in Education Project in 1985, to create educational resources for schools. In 1989, the Citizenship Foundation was founded out of this project. Phillips remains President of the Citizenship Foundation.[5][6]

In July 2006, to the surprise of many people, Lord Phillips of Sudbury announced his intention to resign from the House of Lords at the age of 67 (the average age of members being 68). He criticised the “cascades” of legislation that the Labour government had introduced:

“It is seriously counter-productive. No society can absorb a net increase of statute law of eight or nine thousand pages a year.”

He said he would pursue other interests, and would no longer be just a “weekend husband” to his wife.

He had wanted to vacate his seat in the House of Lords, revert to being known as Mr Phillips, and allow “new blood” from his party to take his seat. However, although hereditary peers may disclaim their titles under the Peerage Act 1963, life peers are unable to renounce their titles, and continue to hold them for life. Therefore, Phillips took leave of absence from the House, meaning he was unable to attend or vote, but could return at a month’s notice. There was not automatically a seat for a new Liberal Democrat peer in the House.

In 2009, Phillips's leave of absence ended, and he has since begun to attend and speak in the House of Lords again. With the introduction of The House of Lords Reform Act in 2014, which allows life peers to resign from the House, Phillips finally resigned on 7 May 2015, the day of the General Election.

Phillips states that he is a supporter of Israel, and offered to fight for Israel in the 1973 Arab–Israeli War. But visiting Israel, the West Bank and Gaza for the first time in 2001, and a number of times since, has altered his view. He believes Israel's controls on Gaza are contrary to international law and simple morality, and that international action on the Gaza situation is in the interests of Israel.[8] Phillips has called for economic and cultural sanctions on Israel.[9]

Jewish Chronicle articles have been critical of Phillips views, suggesting that he is being critical of Jews as well as of Israel.[10][11]